Answers

Best Answer: It depends on the (cooling) capacity of your system. A 1.5Ton system will need only about 2 lbs of refrigerant. A 3.5Ton system will need about 6 lbs. I sell R22 for $50/lb. I figure that covers all the overhead it took to get the stuff to your door.......

The only leak "spray" I'm aware of comes in a can resembling a spray can but it is installed in the system with the refrigerant. Its designed to plug those tiny tiny holes that develop in evaporator coils that cannot be welded. Some guys like it, others won't touch it.
I've used it because the customer asked for it. -Its not cheap. $60 for 1 can. -and you only get one shot to install it. If you eff it up thats it.

After you locked down the other question I could no longer put anything else on it. (thanks very much for best answer -I don't know if it was best, but thanks)
If the guy used a $15 contactor, call him back and tell him to take that one off and get an American unit. The $15 one is a cheapazz Chinese unit. It WILL fail before the summer is good and hot. guaranteed.

Really? Is there ice on the suction line? Is the air filter clean? is there 500fpm across the coils? Is the air coming off the condenser 30 degrees above ambient? Never heard of Leak Proof Spray, only leak detection spray. Get a second opinion.